Bolitoglossinae

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Introduction

Members of the subfamily Bolitoglossinae occur in western North America, Central America and South America. All of the tropical representatives are included within a single clade (supergenus Bolitoglossa) that has undergone an extensive evolutionary radiation in the New World tropics, including highly arboreal and fossorial groups (Wake and Lynch, 1976). Convergent and parallel evolutionary origins of webbing of the feet are observed in several genera, with the most extensive webbing found in arboreal and semiarboreal members of the genus Bolitoglossa (Wake and Lynch, 1976; Alberch, 1981; Wake, 1991; Parra-Olea et al., 2004). Convergent and parallel evolutionary trends are observed also for elongate, fossorial forms among the tropical genera Lineatriton and Oedipina and the temperate supergenus Batrachoseps (Parra-Olea and Wake, 2001).

The supergenus Bolitoglossa contains about two-thirds of plethodontid species and 40% of all species of salamanders. The genus Bolitoglossa represents the largest and most widely distributed genus of salamander, with over 90 species, or about 17% of all recognized salamander species (AmphibiaWeb: Amphibian Facts). The supergenus Batrachoseps is comprised of a single genus (Batrachoseps) with two subgenera recognized, Batrachoseps and Plethopsis, which are restricted to the west coast of North America.

Characteristics

Diagnosis

A unique synapomorphy of Batrachoseps , Bolitoglossa is loss of one pair of chromosomes (N=13).

Detailed Characteristics of the Subfamily Bolitoglossinae

Morphological characteristics detailed below are summarized from Lombard and Wake's (1986) phylogenetic analysis of major plethodontid lineages with special emphasis on evolution of feeding mechanisms. These characteristics are useful in combination for distinguishing bolitoglossine salamanders from other plethodontids, although the characteristics listed are not synapomorphies of the subfamily Bolitoglossinae.

Tongue and Hyobranchial Apparatus

All bolitoglossines have attached projectile (Batrachoseps) or freely projectile tongues (i.e., lack the genioglossus muscle and anterior connective tissue; Lombard and Wake, 1986). The hyobranchial skeleton lacks a urohyal, has an expanded basibranchial, and radii that are closely attached to and continuous with the basibranchial. The epibranchial is relatively longer than the basibranchial and first ceratobranchial. The second ceratobranchial is larger in diameter than the first ceratobranchial and constitutes the primary force-transmitting element in the movement of the tongue. The rectus cervicis profundis muscle is folded dorsally near its anterior end. The slip in the rectus cervicis superficialis has been lost. The omohydoideus, genioglossus, and circumglossus have been lost. The intraglossus is attached to the anterior end of basibranchial, lingual cartilage, or equivalent, or to the anterior end of the glossal ligament, ventral to the basibranchial. The basiradialis muscle may be present or absent. The hyoglossus muscle has a complete anterior section and posteriorly-oriented fibers in the posterior section. The suprapeduncularis muscle is present. The ramus hypoglossus bifurcates posteriorly, between the attachment of the first ceratobranchial to the basibranchial and to the epibranchial.

Epibranchial Number

Embryos have a single epibranchial.

Tail Autotomy

Cutaneous wound healing in the tail occurs, there are 2 caudosacral vertebrae, the first caudal vertebra is specialized, and tail breakage is localized.

Brain Stem Motor Column

There is only one class of brain stem motor column cells.

Jaws, Cranial Osteology and Structure of the Inner Ear

The bony shelf of the preorbital process is absent. A distinct lateral spur on the parietal is present. Premaxillary bones are relatively slender, and the intermaxillary gland is posterior to the pars dentalis. The periotic canal is straight or with a dorsal loop after it leaves the periotic cistern. Growth of otic semicircular ducts is nearly isometric.

Chromosome Number

The diploid number of chromosomes is 26.

Development

Development is direct.

Classification

Traditionally, Plethdontidae was subdivided into two subfamilies, Desmognathinae and Plethodontinae, the latter of which was further subdivided into the tribes Bolitoglossini, Hemidactyliini and Plethodontini (Wake, 1966; Lombard and Wake, 1986). More recent phylogenetic analyses of whole mitochondrial genomic DNA sequences (Mueller et al., 2004; Macey, 2005) and combined mitochondrial DNA, nuclear DNA and morphology (Chippindale et al., 2004) reject the monophyly of these traditional groupings. Consistent with their phylogeny, Chippindale et al. (2004) recommended several taxonomic changes that required minimal changes to traditional taxonomic arrangements, including elevating the tribe Bolitoglossini to the subfamily Bolitoglossinae.

Discussion of Phylogenetic Relationships

Lombard and Wake (1986) postulated a sister-group relationship between Batrachoseps and the supergenus Bolitoglossa based on 30 morphological characters with an emphasis on the hyobranchial skeleton and musculature of the feeding system. Subsequent phylogenetic analyses of combined mitochondrial DNA and morphology (Jackman et al., 1997) and combined mitochondrial DNA, nuclear DNA and morphology support this relationship (Chippindale et al., 2004). In contrast, Bayesian and maximum likelihood analysis of whole mitochondrial genomic DNA sequences recovered a sister-group relationship between Batrachoseps and Hemidactylium scutatum, while parsimony analysis placed Hemidactylium basal to all other plethodontids (Mueller et al., 2004; Macey, 2005).

Parra-Olea, G., M. Garcia-Paris, and D. B. Wake. 2002. Phylogenetic relationships among the salamanders of the Bolitoglossa macrinii species group (Amphibia: Plethodontidae), with descriptions of two new species from Oaxaca (México). Journal of Herpetology 36:356-366.

Wake, D. B. 1966. Comparative osteology and evolution of the lungless salamanders, family Plethodontidae. Memoirs of the Southern California Academy of Sciences 4:1-111.

Wake, D. B. 1991. Homoplasy: the result of natural selection, or evidence of design limitations? American Naturalist 138:543-567.

Wake, D. B., and P. Elias. 1983. New genera and a new species of Central American salamanders, with a review of the tropical genera (Amphibia, Caudata, Plethodontidae). Contributions in Science, Natural History Museum of Los Angeles County 345:1-19.

Wake, D. B. and J. F. Lynch. 1976. The distribution, ecology and evolutionary history of plethodontid salamanders in tropical America. Natural History Museum of Los Angeles County Science Bulletin 25:1-65.

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